The Cotton Belt commuter line and a downtown Dallas subway were Dallas Area Rapid Transit's billion-dollar babies — born on the same night, Oct. 25, 2016.

But as DART officials this week ironed out the finer points of the $1.1 billion Cotton Belt, which will run from Plano to DFW International Airport, the project's twin — dubbed "D2" — is still up in the air.

The subway's scheduled 2024 opening might be optimistic at this point. The project still depends on a $320 million grant administered by the Federal Transportation Administration — a source of funding that has slowed.

"The administration changed, and it has not been very favorable to transit," said Lee Kleinman, a Dallas City Council member and chairman of the city's mobility committee. "It's anybody's best guess as to when they start funding these grants again."

Lee Kleinman, Dallas City Council member and chairman of the city's mobility committee, has long been a proponent of the Cotton Belt.

Although several Dallas City Council members criticized the Cotton Belt, DART saw both projects as important to its rail system's future. D2 was meant to help unclog the current light rail system, where all four lines run on a single set of tracks downtown. And DART's northern cities had long sought an east-west connection to the airport.

The bulk of the funding for Cotton Belt is a $908 million federal loan. DART, which is primarily funded by sales tax revenue from its member cities, is on target to close the loan in November.

DART chose to fund D2 with bonds and the grant so it could be built at the same time. DART's backup financing plan could be to issue capital appreciation bonds, which carry risk and threaten to saddle future generations with a massive bill.

DART executive director Gary Thomas discusses the proposed Cotton Belt rail line with residents during a meeting in downtown Plano in August 2016.

(Jason Janik/Special Contributor)

Gary Thomas, DART's president and executive director, said that "there's a little different path" for both projects because of the difference in financing.

But that was what some Dallas leaders feared in 2016. They warned that DART's reliance on a federal grant for D2 would, in essence, lead to the agency's prioritization of the Cotton Belt.

Originally, much of what DART needed was to be an above-ground line, likely along Young Street. But pushback from residents and developers near the Dallas Farmers Market forced planners to rethink the route and put it underground. DART found a path underneath Commerce Street to be more palatable. However, the speed bump in site selection was costly to the grant application.

"D2 has been a very, very robust planning process with lots of input," said Thomas, who initially hoped to make D2 a reality soon after the proposed Dallas-to-Houston high-speed rail's 2021 target opening. "The public didn't agree with our premise. The City Council said they wanted a change, and the board agreed."

But downtown has also been changing. The growing downtown population has led to a focus on shorter trips, Downtown Dallas Inc. President Kourtny Garrett said.

"We still see a benefit for the region and for regional light rail," she said, noting a focus on improving traffic in the group's recently updated 360 Plan. "We're really looking for alternative transportation, public transit with DART to focus on streetcars, how to better use the bus system, even scooters to come into play. And of course continuing with the second rail line as we learn more about what's happening at the federal level."

She said Downtown Dallas Inc. is working closely with DART and area stakeholders on the design and location of D2 stations to ensure the system integrates well with downtown.

Kleinman, a proponent of the Cotton Belt, said he wants to see D2 move forward to help unclutter the four-stop stretch between Pearl and West End stations where Blue, Green, Orange and Red light rail lines all run.

"We need it probably more than anything," Kleinman said. "Having one track for all four lines is truly a flaw."